Living Off Grid: Insulated Concrete Forms

A lot has been written about insulated concrete forms (ICFs) the past few years but mostly by manufacturers. We have two winters and one summer under our belts now and it’s time to weigh in from a home owners point of view. Our temperature extremes run from 105F in the summer to -9F in the winter so we have a pretty good idea of how well this insulated building system has performed.

ICFs are usually 2’ long x 1’ high x 2 1/4” wide Expanded Polystyrene panels that are stackable and fit together like Legos. Plastic inserts hold the inside and outside panels together creating a space to be filled with concrete. The end result is a concrete wall with 2 ¼” insulation on both the inside and outside.

I’m not going to get into a lot of the selling points for ICFs in this blog. I’ll let the marketing departments and you or your contractor figure out what is and isn’t true about the so called advantages for using this system to build the walls of your home. I will say there are some advantages for sure but not all of their marketing claims are accurate. I would rather speak to my own experiences as a home owner and general contractor about the results we got in our home.

There is no question this is a good building system over all but as with any system there are items in both the Plus and the Minus columns. Those are what I would like to focus on for this article.

Plus:

ICFs are fairly easy to work with and I would put more emphasis on labor than skill for their assembly. That’s good news for people who may want to do the work themselves or for contractors who are not familiar with this system. However, the marketing claims of “fast and easy erection” will only be realized by experienced installers.

ICFs are great for soundproofing. Our home is very quiet but keep in mind that part of the reason is the large amount of insulation we had blown in our attic, not just the ICF walls.

Properly braced they work just fine as concrete forms.

VOC free – no contaminants are released into the air we breathe inside our home and that is more important than ever before with the new energy codes that require our homes to be sealed.

More resistant to mold and rot than traditional wood framing

The insulation is more continuous than wood stud framing with insulation between the studs.

Electrical and plumbing turned out to work pretty well with this system.

Minus:

Even though the EP insulation is insect resistant, it has been discovered that ants sometimes like to remove the foam beads and haul them away for nest building elsewhere.

You will have wide or “thick” walls. If you trim out your doors and windows with wood like we did you will pay more for your millwork. Our window sills are 12” wide. Nice to set plants on but more expensive.

The GWB fastened okay on the inside but the siding was more difficult to fasten on the exterior than traditional wood framing.

When you pour the walls 8’ high all the way around your house like we did you eliminate all further access to the inside except through doors and windows. Plumbing lines will have to be backfilled by hand. Sand and gravel will have to spread by hand. Remember you are not going to have a foundation wall. Your ICF wall will go from the footing to the top plate.

My biggest gripe: This is the kicker for me – In all exterior building walls there is a hot/cold line, the place where the inside and outside temperatures meet and even out. That usually occurs at or near the insulation. In this wall system it occurs somewhere in the middle of the concrete wall.

That doesn’t work well in colder climates. We should be heating the concrete mass from the inside and the concrete will help hold that heat and reflect it back into the house, but with this system we have 2” of foam between your heating source and the concrete. What you end up with is an extremely even inside temperature that rarely fluctuates which would be fine in a more moderate climate but not so good in a cold climate. You end up using more heat than you should have to in order to push the cold line back to the outside. I would rather see the hot/cold line at the outside insulation layer.

In the hot summer months our house stays in the lower 70s no matter what which is good, but in the winter months you really have to pour the heat on if you want to raise the temperatures and keep them there.

I believe it would be better to have poured the concrete walls and put 4” of insulation on the outside or purchased the ICFs that are 2” of insulation on the inside and 4” on the outside. If I had it to do over, that’s what I would have done.

What we have works and is acceptable but one of the two options above would have been better.

Having the insulation on the inside makes the temp fluctuate more. This is good if you leave it unheated for hours as you go to work, perhaps. However, if you have a variable heat source like solar or wood, more heat storage is a good thing.

Tom H

4/14/2012 3:42:42 AM

i think the unsustainable ingredients could be offset by the significantly longer life span of this type of construction. Roman concrete structures not protected from the elements still stand thousands of years after construction. Science tells us foam and plastics will last eternity in a land fill. Imagine how much longer they will last under brick or concrete siding. The only structural thing to wear out in this type of construction should be the roof.

David Reed

4/13/2012 3:07:00 PM

You mentioned nothing about the embodied energy of concrete, the toxins in the creation of the Styrofoam, the amounts of plastics in the clips that hold the ICF's in place, all in all beyond the great insulation this provides, every bit of materials that go into ICF's are NOT SUSTAINABLE!!!

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